(1). Field of the Invention
The present invention relates to a novel hydrophilic carbodiimide. More particularly, the present invention relates to a hydrophilic dicyclohexylmethanecarbodiimide which is improved in reactivity and storage stability and thereby is easy to handle as a crosslinking agent for hydrophilic resins.
(2). Description of the Prior Art
Hydrophilic resins are in use in many applications such as coatings, inks, textile treatment agents, adhesives and the like. They, however, are in inferior to lipophilic resins in water resistance because they have hydrophilicity.
To improve the water resistance of a hydrophilic resin, it has been conducted to use a crosslinking agent together with the resin. As the crosslinking agent, there is used a compound having a methylol group, ethyleneimine group, epoxy group, isocyanate group or the like.
Some of such conventional crosslinking agents are excellent in imparting water resistance of hydrophilic resins. In recent years, hydrophilic resins have come to be used in wider applications and more excellent properties are required. In many cases, hydrophilic resins are required to have crosslinkability at low to ordinary temperature. Hydrophilic resins are also required to have good storage stability after the crosslinking agents are mixed thereinto, and no hazardous effects to human, and so on. The above crosslinking agents, however, are not fully effective when used in hydrophilic resins at low to ordinary temperature, and incapable of giving hydrophilic resins sufficient water resistance, and, moreover, they are not sufficiently safe in view of the hazard to human health (skin stimulation etc.).
Recently, attention has been paid to those carbodiimide compounds which are used in amidation between carboxyl group and amino group, peptide synthesis from amino acid, etc., because such carbodiimide compounds can act as a crosslinking agent for hydrophilic resin and have high safety.
With respect to the technique of using a carbodiimide compound as a crosslinking agent, there are disclosed a polycarbodiimide derived from isophorone diisocyanate and a method for crossliking of hydrophilic resins using the polycarbodiimide, in, for example, JP-A-59-187029 and JP-B-5-27450.
In the above method, the crosslinking of a hydrophilic resin is conducted by utilization of a reaction between the carbodiimide group of a polycarbodiimide and the active hydrogen of an active hydrogen compound, for example, a reaction between the carbodiimide group of a polycarbodiimide and the carboxylic group contained in a hydrophilic acrylic resin.
The above-mentioned carbodiimide compound derived from isophorone diisocyanate, however, is highly reactive and has had problems in that (1) the storage stability after addition to a hydrophilic resin is low because of the high reactivity and (2) the time from addition to the hydrophilic resin, to application of the mixture is short.
In JP-A-7-330849 is described a carbodiimide compound derived from tetramethylxylylene diisocyanate, which has good storage stability after addition to a hydrophilic resin. In this carbodiimide compound derived from tetramethylxylylene diisocyanate, the reactivity of the carbodiimide group is low and, therefore, the storage stability of the compound after addition to a hydrophilic resin is superior to that of the carbodiimide compound derived from isophorone diisocyanate. In using the carbodiimide compound derived from tetramethylxylylene diisocyanate, however, a long time is taken for the crosslinking and there are cases that no sufficient effect is obtained when the crosslinking is conducted at low temperatures and in a short time.
As a carbodiimide compound capable of exhibiting a sufficient effect in crosslinking at low temperatures and in a short time, there is disclosed, in JP-A-10-30024, a multi-branching type carbodiimide compound having four or more branches each having a carbodiimide group. This multi-branching type carbodiimide compound, as compared with straight-chain carbodiimide compounds, can give a high crosslink density even in the crosslinking at low temperatures and short time; however, the compound has no good storage stability after addition to a hydrophilic resin and its storage period is shorter than that of straight-chain carbodiimide compounds.